Add OpenGL context to Viewer.

tools/viewer/sk_app/win/Window_win.cpp

 /*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #include "Window_win.h"
 
 #include <tchar.h>
 #include <windows.h>
 #include <windowsx.h>
 
 #include "SkUtils.h"
-#include "VulkanWindowContext_win.h"
+#include "../GLWindowContext.h"
+#include "../VulkanWindowContext.h"
 
 namespace sk_app {
 
 Window* Window::CreateNativeWindow(void* platformData) {
     HINSTANCE hInstance = (HINSTANCE)platformData;
 
     Window_win* window = new Window_win();
     if (!window->init(hInstance)) {
         delete window;
         return nullptr;
@@ skipping 231 matching lines @@
 
 void Window_win::setTitle(const char* title) {
     SetWindowTextA(fHWnd, title);
 }
 
 void Window_win::show() {
     ShowWindow(fHWnd, SW_SHOW);
 }
 
 
-bool Window_win::attach(BackEndType attachType, const DisplayParams& params) {
-    if (kVulkan_BackendType != attachType) {
-        return false;
-    }
-
+bool Window_win::attach(BackendType attachType, const DisplayParams& params) {
     ContextPlatformData_win platformData;
     platformData.fHInstance = fHInstance;
     platformData.fHWnd = fHWnd;
 
-    fWindowContext = VulkanWindowContext::Create((void*)&platformData, params);
+    switch (attachType) {
+        case kNativeGL_BackendType:
+        default:
+            fWindowContext = GLWindowContext::Create((void*)&platformData, params);
+            break;
+
+        case kVulkan_BackendType:
+            fWindowContext = VulkanWindowContext::Create((void*)&platformData, params);
+            break;
+    }
 
     return (SkToBool(fWindowContext));
 }
 
 void Window_win::inval() {
     InvalidateRect(fHWnd, nullptr, false);
 }
 
 }   // namespace sk_app